Travelling wave discharge tube arrangements utilizing delay lines



March 18, 1958 P. GUENARD ET Ax. 2,827,588

y TRAVELLING WAVE DISCHARGE TUBE ARRANGEMENTS UTILIZING DELAY LINESFlled Aprll 17; 1952 3 Sheets-Sheet 1 (s Y V/ @gf ZLH #i 3 Y *i f. I@ummm mm March 18, 1958 P. GUENARD ET AL 2,827,588

TRAVELLING WAVE DISCHARGE TUBE ARRANGEMENTS UTILIZING DELAY LINES Filed`April 17, 1952 3 Sheets-Sheet 2 49 MIU/H //J\ geen/vis March 1'8, 1958P. GUENARD ET A1. 2,827,588

TRAVELLING WAVE DISCHARGE TUBE ARRANGEMENTS UTILIZING DELAY LINES FiledApril 17, 1952 5 Sheets-Sheet 5 i l z: il] L11-s L Il ri iuj] I E* onl:: Lila I 3]: .I LID m :Il j] :3 :im i

IC. /j 1^' "6 T" 5 effec" 60g/Hlth Has/y 71s United States aterra itiicen Patented Mar. 18, 1958 TRAVELLWG WAVE DISCHARGE TUBE AR- RANGEMENTSUTLZENG DELAY LINES Pierre Gunard, Robert Warnecke, and RenBerterottiere, Faris, France, assignors to Compagnie Generale deTelegraphie Sans Fii, a corporation of France This invention relates totravelling wave discharge tube arrangements of the kind in which a delayline is used in association with an electron beam discharge tube.

The invention is illustrated in and explained in connection with theaccompanying drawings.

Figure l is a plan View of Figure 2 showing a prior art delay line ofthe interdigital type;

Figure 2 is a cross-sectional view taken along line 2f-2 of Figure l;

Figure 3 is a top plan View of a delay line of the interdigital type inaccordance with the present invention;

`Figure 4 is a cross-sectional view taken along line 4 4 of stillanother embodiment of a delay line in accordance with the presentinvention;

Figure 5 is a cross-sectional view taken along line 5-5 of Figure 4;

Figure 6 is a cross-sectional view taken along line 6*-6 of Figure 7showing a still further embodiment of a delay line in accordance withthe present invention;

Figure 7 is a bottom plan view of the delay line illustrated in Figure6;

Figure 8 is a longitudinal cross-sectional View through a travellingwave tube utilizing a delay line in accordance with the presentinvention of the type illustrated in Figures 6 and 7; and

Figure 9 is a cross-sectional view taken along line 9-9 of Figure 8.

The so-called symmetrical nterdigital line is most advantageous for usein a travelling wave tube arrangement of the kind referred to. This formof line is illustrated in Figures l and 2 which are mutuallyperpendicular views of part of such a line.

As will be seen from Figures l and 2, which are respectively plan andlongitudinal sections, such a line consists of two supports 1, 2 onwhich are disposed interleaved ngers 3, 4 for example metal bars orplates. In a travelling wave tube of the kind referred to, such a linemay be disposed parallel to a plate 5, an electronic beam being injectedinto the space 6.

In the co-pending application of Warnecke and Gunard Serial No. 275,928,filed March l1, i952, an examination is made of the propagation of Wavesin the zig-Zag guide path which is bounded by the fingers of such aline, and it is indicated that, for a certain direction of propagationof energy, there exists an infinity of waves being propagated at speedssuch that their phase shift between the points 7 and 8 representing thecentres of successive lengths of the zig-zag is given by the generalexpression:

\[/=g;-S1r+21rm (l) Where s is (to a close degree of approximation) thelength of a linger, A is the wavelength in vacuo, and m any positive ornegative whole number including 0.

It is likewise indicated in said co-pending application that it isadvantageous to select for interaction with the electron beam, thefastest of the possible waves available 2 i. e. the wave correspondingto a phase angle ,lf which is as low as possible in absolute value. Itfollows from the Expression l that for a linger length of the order ofM4, the lowest possible value of gb is of the order of for r11-:0, andthe next higher value is of the order of for m=l. The positive sign hereindicates that the wave is propagated in the same direction as theenergy, and the negative sign indicates that the wave and the energy arebeing propagated in opposite directions. In View of the fact that inamplifiers, in which the energy is propagated in the direction of thebeam, the interaction requires a component of positive sign, thesymmetrical interdigital line is not advantageous for application toamplifers, because the first wave utilisable corresponding to the phaseshift is not a predominating component, the greatest amount of energybeing carried by the wave corresponding to the phase shift which ispropagated in the undesirable negative direction. For this reason it isproposed in the aforesaid co-pending application to introduced into theline a dissymmetry which favours the wave of positive sign to thedetriment of the fundamental wave of negative sign.

The present invention seeks to solve the problem thus raised in adifferent manner, without requiring the introduction of any dissymmetryinto the line.

The invention is characterised in that the line is so constructed thatoutside the region of the beam, that is to say at the corners of thezig-zag guide formed between the fingers of the line, the wave passesthrough guide elements which introduce a positive or negative phaseshift supplementary to the variation of phase undergone by the wave inthe course of its propagation, that is to say behaving, at ultra-highfrequencies, as the equivalents of reactive impedance elements.

The elements may be arranged to act as the equivalents either ofinductances or of capacities and although the action is different in thetwo cases the linal effect obtained is the same. If a guide element inquestion behaves like an inductance, it is arranged to introduce asupplementary phase shift comprised between vr 371' "iand so that thephase shift of corresponding to the negative slow mode is broughtbetween O and 1r. If the element behaves like a capacity it is arrangedto introduce a phase shift between so that the phase shift of of thepositive fast mode is brought between O and 1r. In

both cases there is therefore obtained a positive mode, the phase shiftof which is between V and 1r, that is to say it corresponds to thelowest value possible, as is vention may be introduced into the zig-zagguide by simply moving apart the combs shown in Figure 1, in

suchmanner as to increase the distance between the ends of theVfingersendjthe supportef the opp'ositef'corn'b, as

shown in Figure 3. Here the finger length is made as 3/s)\, witha'distance of A/'S'between the ends of the vfingers and the support ofthe opposite comb. VThe space 13, 'the dimension of whichl measured inthe V4direction of the width of the line isV less than M4,Vbehaves-.like an inductance inserted in series in the zig-zag' guide.-This dimension of the space 13 could be made-greater'than M 4, Yso asto .obtain the equivalent of 'a capacity,`butthis alternative is lessadvantageous, because 'for practical reasons of construction it isadvantageousto/make the totalV line width as small as possible.

`VFigures 4 and 5 illustrate diagrammatical v embodiment. Here thefingers 3, 4 are iiXe'dmo'n V'supports 9, 10 having transverse"dimensions greater than those of the fingers and themselves fixed onthe general supports 1, 2, Vso thatY the profile off-each lcomb thas a Yway there is obtained the equivalent of a considerable induCtance, witha relatively'fsrnall depth for the notches 11, 12. Y Y l Y In order toobtain betterseparationof the region `where the beam is injected fromthe regions where the" supplies mentary vphase shift is effected,V andin order 'to'rvreduele theV width of the line, it'niay bekofadvantageto'bend the fingers of the line so that they YpenetrateV int'ojthe' spaces equivalent Vto the phase-shifting circuits` atthe`ends`1which are bent back "at right-angles t'othe plane-of thejline. A delay line arranged Vin this -wa`y is 'illustrated-*in vFig'-u'res 6` and 7.V Here the fingersv '15, 16,shown rby way of example asrectangular'bars' (Figure "Sis ar'cros'ssectionV andFigure 71a Vviewfrom below), are vrembedded" in s'olid supports 17, '18 fixed on' 'acommon plate 14. These fingers are bent back at9 and120", and'dipjaliternately Y into -the notcheslanfdprovided inathe supports 18 and17k and constituting the 'e'quiva'lentof phaseashi'f'ting quadripolessirn'ilarly't'o` the spaces' 1l3' and-Tlf in Figures 3 and 4. At 5 therehas beerr'shown, "asini-figuresZandA 5, av parallel `electrode defining,together 'thejd'elay line, a space 6 into' which'tlrerbe'am' isinjected, thefla'tt'er thus being well'insulated'from thephase-*shifting* regions 21 and 22:. i

Figure 8 illustrates in' longitudinalsection, jand'Fig-VY, ure 9 insection taken on' theline r9`-"9*in"Fi`gure 81a travelling wave tubehaving crossedmagnetic and electric fields and utilising alineas'illustrated in Figures 6 and 7.

The Various elements are mounted in a vacuum-,tightV metal casing 31ending at the righthndlendfinlazcollector Vanode 32. The coaxial YinputVline 27 for the ultra-high ly a further Y Y -ngerscor'nprisesa thirdportion perpendicular to the is injectedbetween the'elect-r'ode 5,Whichmaybe brought P to a high negative potential by the source 25, andthe.

line 14 which may be connectedfto the ground connec- ,Vtion of the tubeand thusbroug'ltf'ito zero D. C. potential so astoV create in thespace'traversed by .the beam an electrostatic field the lines of forceof "which run lparallel to the'plane of the drawingv'and at right-angles-t'o the trajectory of the beam Y29. 'A magnet, the pole-pieces33,7.34jof whicli'lare` illustrated in Figure 9, createsv a Vmagnetic'field the ylines of force of which fare perpendicular both to the beamand to the preceding electric Vfield.

Some of the fingers 15 of the delay line may, if desired, be made ofresistive material, in order to introduce attenuation into the saidline.

We claim: s y I 1. A Vtravelling'wave electron tube, comprising meansfor producing an electron beam, a delay line having twomutuallyIuncoupledextremities, traversed by an ultrahigh frequencytravelling Wave and comprising a first supportrarid a s'ec'o'ndV supportparallel toA one another and parallel to the-:mean trajectory of saidbeam', a series of parallel fingers .positioned between said supportsand Ving support, so as to becapacitively coupled therewith,

thereby forming. an interdigitalstructure havingvajlongitudinalsyrninetry plane in the direction of said beam.

2. A tuberas clainnedV in claim l, wherein said'supports areprovided-withcavitieseach disposedbetween two adjacent fingers"carriedbyrthesarnesupport, s aid free extremities of fingers carried bys one support penetrating into respective cavities .provided inthe othersupport.

3. A. tube as claimed in `clairn 1s, Awherein each lof said 4. .A tubeasclaimed i-n'clhaim '1,- wherein eachof said l 5. A delay line for atravelling wave tube oftlie type Y in which an electron beam moves inaninteractionpsprace adjacent said line and -inenergy transferrelationship therewith, comprising a viirst. support and-Ya' second sup;

Vport for said delay line lessentially parallel t o eachother, a seriesof parallel iingers positioned between said sup-v ports, each of saidfingers *beingV built so as v to have at least two mutuallyperpendicular portionsrLthveV first porrtion thereof being essentiallyperpendicular to the'plane VVof saidl supports andk the second portionthereof being es -V sentilallydparallell tosaidplane, the jextremitiesof said first portions ybeing alternately carried by'saidrfirst andsecond supports to thereby form a Vdelay .line 'of the :interdigitated`Ytypaa'ndY each vof isaid ngersY terminating with` the free eirtreniitythereof. positioned "adjacent and' spacedff'rinl the support oppositesaid first portionv carrying supportfthe'reof so` a's tobefcapacitivelycoupled there-V with, ythereby'formingan interdigital structure havingVa longitudinal plane of symmetryi in the direction of said beam. 1

Referencesf Cited in iile' of.v this` patent' UNITED STATES kPATENTS

